fix: remove generic package export

[tobiasdiez]

I got the following error with nuxt:

[DEP0166] DeprecationWarning: Use of deprecated double slash resolving ".//index.json" for module request ".//index.json" matched to "./*" in the "exports" field module resolution of the package at D:\Programming\JabRefOnline\node_modules\.pnpm\node_modules\tslib\package.json

(I think this is windows specific)

This is fixed by removing the generic ./* export field.

[jakebailey]

See #135, this was intentionally added

[tobiasdiez]

This talks mostly about older node versions. Should I also delete ./ which is deprecated now for a long time?